1. Field of the Invention
The present invention relates to a method for compensating a position error contained in position information measured from a resolver which is a position sensor used for motor control.
2. Description of Related Art
When a permanent magnet synchronous motor is driven by vector control, accurate position information of a rotor thereof is required. Typically, a resolver (e.g., a pressure sensor) may be used to recognize the absolute position of the rotor. However, due to a difference in the transformation ratios of the resolver, unbalanced excitation signals, existence of inductance harmonic components, and distortion on a signal processing circuit, a magnitude unbalance of signals occurs, thereby causing a periodic error component in the position information. Accordingly, since the motor control performance is degraded, resolvers are limited as to their use and effectiveness in the high-performance field.
In order to reduce such a position error in the resolver, error information which is previously measured by a precise position sensor may be written into a table of a memory, for example, a ROM (Read Only Memory), and a position error may then be compensated based on the error information (hereinafter “the first related art”).
Alternatively, output signals of the resolver may be modeled by using a regression equation, and a recursive least square method may be then used to estimate a model parameter such that an error between model values and the measured signals are minimized, thereby compensating for the output signals of the resolver (hereinafter “the second related art”).
In the first related art, a measurement operation is required to acquire error data which is stored in a table in the memory, and such error data acquired for one sample product does not reflect a deviation between products. Therefore, according to the first related art, an individual zero adjustment needs to be performed for each product thus, required additional computations which slow efficiency and the overall speed of the process.
In the second related art, output signals of the resolver are directly compensated by an estimated signal model. However, since the signals are high-frequency AC values and a complicated analog electronic circuit or a digital signal processing system is required for the compensation process, it is not easy to implement this solution. Furthermore, accurate compensation may be achieved only when the measured position information is synchronized with the calculated error information. Therefore, an individual zero adjustment needs to be performed for each product, similar to the first related art, thus again requiring additional computations which slow efficiency and the overall speed of the process.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.